Torque motors are known in the art and are configured to produce a torque in order to rotate or move a shaft (e.g., a jet pipe) so as to operate a valve, for example a valve used in a direct drive or pneumatic field, such as an electrohydraulic servo-valve.
An example of a torque motor 10 is shown in FIG. 1A (which is provided for illustrative purposes only), and comprises a lower pole piece 12 and an upper pole piece 14, two sets of coils 16, an armature 18 that is pivotally located within the structure of the torque motor 10. The pivoting armature 18 is connected to a shaft 20, a lower end of which (not shown) is configured to move (e.g., left and right) upon rotation of the armature 18. In use, the movement of the lower end of the shaft 20 (e.g., jet pipe) may be used to operate a valve and/or control fluid flow of various types, and other applications as well.
To ensure high performance of the torque motor 10, the components that are used to create the magnetic field around the armature 18 must be manufactured to a high precision, and such that the clearances between the various magnetic parts (e.g., the lower and upper pole pieces 12, 14, the coils 16 and the armature 18) are as small as possible.
To assemble the torque motor 10, the lower pole piece 12 may be opened or divided into two separate parts 12a, 12b, and an additional part 13, called a magnetic shunt, may be used to connect the separate parts 12a, 12b of the lower pole piece 12 when assembling the torque motor 10.
The geometrical features associated with the connections between the separate parts 12a, 12b of the lower pole piece 12 and the magnetic shunt 13 have to be manufactured with a high precision, but also to allow for the change of the material properties caused by stresses in use. This means, for example, that an interference or press fit may not be used due to potential changes of the material properties; therefore, even with high precision methods that use tight tolerances, there will typically be gaps present between these parts.
In the embodiment of FIG. 1A, a setting shim 11 may be provided in order to connect the various parts of the torque motor 10 to a housing 22. In an alternative background embodiment, as shown in FIG. 1B (also provided for illustrative purposes only), a component 23 may be provided that forms a combined magnetic shunt and setting shim. In this embodiment, the same issues may occur, in that the various components must be manufactured with tight tolerances, but may not be provided with an interference or press fit.
It is desired to provide an improved pole piece for a torque motor.